This invention relates to an index signal generator which generates an index signal. The index signal generator is used for a disk drive that handles a recordable medium, and provides the disk drive with hardware compatibility for the same kind of disk drives. For example, a recordable medium is a floppy disk (FD) and a disk drive is a floppy disk drive (FDD).
As well known, FDDs are devices for reading data out of FDs and for writing data in FDs. FDDs have spread to the art of electronic devices and have been used in various electronic devices, for example, a personal computer, a work station, a word processor, and so forth.
One of the reasons why FDDs have widely applied to electronic devices is the data compatibility that users can move data from an electronic device with FDD to another electronic device with FDD by FD. That is, the high data compatibility among FDDs promotes the use of FDDs.
In general, the data compatibility among FDDs are ensured with the hardware compatibility, the standardized track format, and the software (or application) standards. Among them, the hardware compatibility standardizes a magnetic head, a posture of a magnetic head, a generation timing of an index signal and so on.
An index signal is a pulse signal that is generated every a magnetic disk included in an FD rotates in order to indicate a starting position of the disk rotating. The index signal is used for various uses in an FDD and a system of electronic device. For example, the index signal is used for generation of xe2x80x9cReadyxe2x80x9d signal in an FDD. Thus, the index signal is a great contribution to the hardware compatibility among FDDs.
In an FDD of 3.5 inch type, an FD is driven by a pin projecting from a disk table toward the FD so that the magnetic disk is rotated. In this case, the disk table and the rotor included in the FDD rotate together with the magnetic disk so that the rotation of the rotor and the disk table synchronizes with that of the magnetic disk.
An index signal is generated on the basis of a rotation of a rotor if a direct-drive motor is used to drive a disk rotation. For example, a direct-drive motor is a spindle motor.
To detect a rotor rotation, a small magnet is provided with the rotor, while xe2x80x9cHall elementxe2x80x9d is located close to the peripheral surface of the rotor. Hall element is a semiconductor element using a xe2x80x9cHall effect,xe2x80x9d the development of a transverse electric field in a current-carrying conductor placed in a magnetic field. Hall element serves as the current-carrying conductor. Ordinarily Hall element is positioned so that the magnetic field is perpendicular to the direction of current flow and the electric field is perpendicular to both. A voltage occurred at Hall element by Hall effect is called Hall voltage.
Especially, in an earlier FDD, only one pole of the small magnet is exposed to the outside of the rotor. With the structure, during the single rotation of the rotor, the exposed pole of the small magnet passes in front of the Hall element for once.
As the exposed pole of the small magnet approaches the Hall element, the magnetic flux detected by the Hall element increases. When the center of the exposed pole faces to the center of the Hall element, the detected magnetic flux become maximum. As the exposed pole gradually leaves the Hall element, the detected magnetic flux decreases. During these events, the Hall voltage changes in a half period of the sine curve with a certain coefficient. The index signal is generated at a time when a delay time passes since the Hall voltage reaches a predetermined level.
The delay time is set appropriately so that the hardware compatibility among FDDs is obtained. To set the delay time to the appropriate time, the earlier FDD comprises a delay or a delay circuit where a delay time can be varied. The delay time is adjusted after production of the earlier FDD so that the index signal generated in the earlier FDD can meet the hardware compatibility.
However, in the earlier FDD, the delay comprises a variable register and a capacitor, both of which are connected in parallel to each other, besides an analog delay circuit that is formed in an integrated circuit. The variable register and the capacitor make the cost of the earlier FDD high because these are discrete elements. In addition, the adjustment process of the variable register brings about some costs.
The present invention therefore provides an index signal generator comprising a delay without a variable register and a capacitor.
According to one aspect of the present invention, the index signal generator comprises, as the delay, the delay counter that can be set the initial value or the initial counter value. The index signal generator is for generating an index signal and is used to control the rotation of the rotor included in the direct-drive motor.
In detail, the index signal generator according to one aspect of the present invention comprises an original signal generator, a clock, a counter value selector and a counter. The original signal generator generates an original signal every the rotor rotates. The clock periodically generates a clock signal. The counter value selector has the first predetermined number of terminals and holds the second predetermined number of counter values. Terminals are given selection signals from outside of the index signal generator. Each selection signal has a selection value. The counter values are different from one to another. The counter value selector selects, as a selected counter value, one among the counter values in response to the combination of the selection values. The counter starts to count the clock signals generated by the clock in response to the original signal, and stops counting the clock signals and generates the index signal when the number of the clock signals counted by the counter reaches the selected counter value. The counter may be formed with the counter value selector.